The present invention relates to the manufacture of integrated circuits. More particularly, the present invention provides a technique for forming substrates using a high temperature implantation technique. This invention is illustrated using, for example, silicon wafers, but can be applied to other types of substrates.
There are many conventional ion implanter designs. In most of these designs, it is desirable to maintain a cool implant temperature for semiconductor processing applications, where high temperatures often damage integrated circuit device elements and structures. In fact, many conventional designs even include fluid cooling systems, which draw heat away from the implanted substrate to maintain temperatures below 100 degrees Celsius. In some applications, however, it is desirable to allow for the implantation of ions while the implantation target (e.g., silicon wafers) are brought to a higher temperature than is usual for conventional semiconductor processing.
Such implanters have been specially designed for such implantation at higher temperature. These implanters are often expensive and not general purpose. That is, these implanters often cannot be used in an efficient manner for both semiconductor processing applications and special high temperature implantation processes. For example, Hitachi and Ibis Technology Corporation each make a high temperature implantation apparatus. This implantation apparatus is used for a wafer making process known as Separation by Implantation of OXygen, commonly called SIMOX, whereupon a high-dose of oxygen ions are selectively placed within a depth of a silicon wafer to create a Silicon-On-Insulator (SOI) structure. It is often a requirement of this process for the silicon substrate to be heated and kept at approximately 550 degrees Celsius during the implantation. As a result, SIMOX implanters (such as the Ibis 1000 implanter for example) have specially designed wafer holders and wheels that incorporate heating mechanisms. This design is often complex and generally makes the high temperature implanter not general purpose that cannot be used for more general semiconductor purpose implantation in an easy manner.
Alternatively, general semiconductor purpose implanters such as the xR-120 series implant tools from Applied Materials, Inc. have been designed specifically to keep the substrates cooled during implantation (on the order of 40-60 degrees Centigrade) in order to satisfy dopant implant process requirements for semiconductor processing. In fact, the implant wheel is designed with water cooling in the wheel mechanism and thus the wheel surface could not be heated much above 80 degrees Centigrade without severe problems arising. In such implanters, the substrate is placed on a cooled wheel, which draws away heat generated during implantation from the substrate. This general purpose implanter is often difficult to modify to achieve high temperature operation.
From the above, it is seen that an improved technique for implanting substrates at selected temperatures in an efficient manner is highly desirable.
According to the present invention, a technique including a method and apparatus for implanting ion species at high temperature into a substrate is provided. In an exemplary embodiment, the present apparatus has a thermal insulating layer that prevents a portion of thermal energy from being drawn off by a substrate holder. This thermal insulating layer allows a wafer temperature to increase to a selected steady state value during implantation in certain embodiments.
In a specific embodiment, the present invention provides an ion implantation apparatus. The apparatus has a vacuum chamber and an ion beam generator to generate an ion beam in the vacuum chamber. The apparatus also has an implant wheel, in the vacuum chamber, having a plurality of circumferentially distributed substrate holding positions. Each of the substrate holding positions comprises a substrate holder, which includes an elastomer overlying the substrate holder and a thermal insulating material (e.g., quartz, silicon, ceramics, etc.) overlying the elastomer. The present thermal insulating material prevents a portion of thermal energy to be drawn off by the substrate holder, which therefore increases a temperature of the substrate as it is implanted. A steady state value of substrate temperature can be achieved using the present apparatus.
In an alternative aspect, the present invention provides a method for implanting lighter mass particles into a substrate. The method includes providing a substrate holder, which has an elastomer overlying the substrate holder, and a thermal insulating material overlying the elastomer. The method also includes placing a substrate onto the substrate holder. The substrate has a face to be implanted and a backside, which is placed on the thermal insulating material. The method also includes introducing a plurality lighter mass particles through the face of the substrate. The lighter mass particles can be selected from hydrogen particles, deuterium particles, helium particles, or any combination of these and even other heavier particles in some applications. The method also includes increasing a temperature of the substrate, at least partially, during the introducing from a first temperature (e.g., room-temperature) to a higher second steady state value that is greater than about 150 or 200 or 400 or 500 degrees Centigrade. During the step of increasing the temperature, a thermal flux from the substrate is substantially equal to a thermal flux into the substrate at the steady state value.
The present invnetion also provides a method for converting a high temperature implant tool from a conventional implant tool design, such as an xR Series from Applied Materials, Inc. The method includes installing a insulating member on an elastomer layer on a substrate holder, whereupon the insulating member faces a substrate to be implanted. The present conventional implanter can be on a fabrication facility or the like, which makes the present method easy to implement.
Numerous benefits are achieved using the present invention over conventional processes. For example, the present invention provides a novel high temperature implantation technique for general purpose beam line implanters. The technique allows for a high temperature implant using relatively simple hardware features. Additionally, the present invention also provides an easy installation technique for converting a conventional implanter such as an Applied Materials, Inc. xR-120 from a conventional lower temperature design to the present high temperature design, which can be desirable in certain applications. The present invention also provides a control for a high temperature implantation process, where the control occurs by adjusting the roughness and perhaps thickness of the insulating material. The invention also has many other benefits such as efficiency of implant species can be improved for specific species and material modification processes that depend on diffusion processes can be better controlled. Depending upon the embodiment, one or more of these advantages may exist. These and other benefits will be described throughout the present specification.
These and other embodiments of the present invention, as well as other advantages and features, are described in more detail in conjunction with the text below and attached Figs.